The present invention relates to a method of recovering non-volatile metals from material in dust form containing metal oxides. More particularly, the invention may be employed in the manufacturing of chromium from chromiferous metal oxides in dust form.
When refining metal melts according to conventional methods considerable quantities of metal oxide dust are obtained. This dust is normally recovered from the exhaust gases by means of flue gas filters of the like. In the Nordic countries alone about 50,000-60,000 tons per year of such metal oxide dust is obtained.
Even after being recovered, the dust has for a long time constituted a major problem from the environmental point of view, since it contains considerable quantities of heavy metals and also toxic chromium compounds. Heretofore, the dust has been stored as waste and dumped since no technically or economically feasible processing methods have been discovered. In this regard, U.S. Pat. No. 4,072,504 discloses a method of reducing metal oxides including the step of pre-reducing the oxides with the reducing gases released during final reduction. The present invention represents an improvement over the method disclosed in said U.S. Pat. No. 4,072,504 in that the pre-reduction step disclosed therein is neither necessary nor desirable and also because the present invention is particularly suited for the treatment of waste dust (which treatment is not mentioned in the U.S. Pat. No. 4,072,504.